Medical Physicist, Radiation Physics Section Biomedical Physics - PowerPoint PPT Presentation

By Saad Aldelaijan Medical Physicist, Radiation Physics Section Biomedical Physics Department King Faisal Specialist Hospital & Research Centre

 About the competition  Contouring stage  Arc geometry  Optimization  Results  Conclusions

 Case selection  Peripheral targets  Inhomogeneous shape  Proximity to organs at risk  The criteria  In general, the criteria is well chosen  Constraints on the right side of the patient were difficult to achieve  I found that some objectives were easily “over” achieved

Structure Points Target (CI , HI, others) 45 Heart 20 Left lung 19 Right breast 6 Right lung 5 Spinal cord 5 Total: 100

 Intensity modulators:  MLC Speed (Max speed 2.5 cm/sec)  Dose Rate (0-1400 MU/min)  Gantry Speed (~4.8 deg/sec)

 Made the structures “high resolution”  Used partially segmented OARs  Used conformation structures (rings)

 Eclipse Ver 13.6 (AAA 11.0.31, TrueBeam)  Limitations:  Target inhomogeneity  multiple field sizes per target  Sparing ipsilateral OARs  isocentre positioning  Sparing contralateral OAR’s  limiting gantry rotation  MLC over-carriage max travel of 14.5 cm  Therefore, I used all available assets (nine coplanar partial arcs) @ 6 MV FFF

290  130 CW Gantry Collimator 5 deg

119  330 CCW Gantry Collimator 355 deg

290  45 CW Gantry Collimator 5 deg

179  70 CCW Gantry Collimator 355 deg

295  75 CW Gantry Collimator 5 deg

75  295 CCW Gantry Collimator 5 deg

82  170 CW Gantry Collimator 355 deg

170  82 CCW Gantry Collimator 355 deg

179  95 CCW Gantry Collimator 355 deg

 Start with targets and rings only:  SC + SC ring + overall ring  add axilla  add breast  add OARs  Try to be patient!

 Pause the optimizer until the cost function “plateaus”  At the “odd number” steps  At the beginning of each phase (calc resolution)  Re-optimize: using the current plan dose as an intermediate dose for optimization

 If your target priorities are P: 100%  Lt Lung: ▪ 95 %  15 % vol max: 2000 cGy ▪ 80%  mean: 700 cGy  Rt Lung: ▪ 80 %  3 % vol max: 500 cGy ▪ 50%  mean: 100 cGy  Rt Breast: ▪ 90 %  5 % vol max: 200 cGy ▪ 50%  mean: 75 cGy  Heart: ▪ 35%  mean: 400 cGy  Spinal cord: ▪ 40%  0% vol max: 600 cGy ▪ 40%  mean: 150 cGy

PTV L Lung Spinal Cord R Lung Heart R Brst

Structure Min dose (cGy) Max dose (cGy) Mean dose (cGy) PTV_TOTAL_EVAL 3868.8 5579.6 5118.7 Heart 48.9 4931.7 388.5 Left lung 69.2 5228.1 973.5 Right breast 0.0 847.9 47 5.0 2363.0 103.7 Right lung Spinal cord 22.2 895.6 139.1

Structure Available Points My score Targets (coverage, conformation, 45 42.43 homogeneity, hotspot) Heart 20 20 Left lung 19 17.62 Right breast 6 3.54 Right lung 5 5 Spinal cord 5 5 Total: 100 93.6

 General:  Understand the criteria to score more  Make a quick table for points/organ  Contouring:  Use high resolution structures  Use conformation structures (rings)  Use partially segmented structures for increased OARs sparing  Geometry:  Nine coplanar partial arcs @ 6 MV FFF  SC (2), Axilla (2), Breast (4) and (1 ) “overall”  Optimization:  Start with SC+rings , add axilla, add breast, then the rest  Try to be patient!